In the electronics art, smaller often means better. In the quest to provide smaller electronic appliances, the electronics industry seeks electronic components that are smaller than predecessor components. The capacitor (a dielectric material sandwiched between two conductors) represents one electronic component that has substantially shrunk in this quest. However, current practice relies largely on individually mounting and soldering discrete surface mount capacitors onto the surface of printed circuit boards. Despite the advances in capacitor miniaturization, each surface mounted capacitor still occupies a significant fraction of the circuit board surface area, and requires substantial cost to place and solder onto the board. For example, a typical cellular telephone contains over 200 surface mounted capacitors connected to the circuit board by over 400 solder joints. The ability to integrate or embed capacitors in circuit boards during manufacture of the circuit boards would provide substantial space and cost savings over surface mounted capacitors. Unfortunately, efforts to make capacitors that can be integrated or embedded into circuit boards have produced capacitors that have small capacitance (typically less than 10 picofarad/mm2) and thus can only replace a small percentage of the capacitors, as most need to be larger than 100 picofarad/mm2.
Other efforts have resulted in structures and processes that are not amenable to the needs of high performance circuitry. Printed circuit boards typically contain multiple layers of copper sandwiched between a glass-reinforced polymer. The copper is patterned to form the conducting elements of the circuit, and the polymer provides dielectric isolation and mechanical robustness. Since polymers are inherently low dielectric constant materials, parallel plate embedded capacitors formed within the conventional polymer circuit board do not offer high enough capacitance density. Although very high dielectric constant ceramics are available, they are typically too rigid to be mechanically compatible with organic printed circuit boards.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale, or to the same scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.